24 August Stoichiometry Recitation

# 24 August Stoichiometry Recitation - Georgia Institute of...

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Georgia Institute of Technology | CHEM 1310 | Fall Semester 2009 | Recitation Assignment Week of 25 August 2008. The Fundamentals and Stoichiometry Recitation Worksheet Fundamental Principles and Terminology Avogadro’s Number 1 mole = 6.022 x 10 23 molecules : Used to represent the amount of a given atom as a basis for comparison with other atoms. Atoms have different masses because they have differing numbers of electrons, protons, and neutrons; therefore, atoms cannot be compared directly. This measure takes into account this differing number allowing for a comparison of the relative number of atoms. Atomic Weight Weighted Atomic Mass = (Isotope 1)*(Percent Abundance) + (Isotope 2)*(Percent Abundance) + (Isotope 3)*(Percent Abundance) + … + (Isotope n)*(Percent Abundance) : Each atom has a specific weight based upon the number of protons, electrons, and neutrons. The atomic weights of each atom were determined using Carbon-12 as a comparison. The weights reported on the periodic table are actually weighted atomic masses because of the presence of isotopes (variations of atoms with the same number of protons and electrons, but a different number of neutrons). The atomic weights of each atom are used to determine the formula weight or molecular weight of chemical compounds. Formula Weight : Used to present the number of grams in one mole of an ionic compound. This is the combined sum of all of the atomic masses of the atoms and their relative proportions. Atom No. Weight of Atom Example: Na 2 CO 3 Na atoms 2 23.00 g 46.00 g Combined Weight C atoms 1 12.011 g 12.011 g O atoms 3 16.00 g 48.00 g SUM 106.01 g Therefore, the formula weight for one mole is 106.01 g. Generally, the formula weights are written in g/mol. Thus, for Na 2 CO 3 the formula weight is 106.01 g/mol. Molecular Weight: The same as formula weight but specific to covalent compounds. Covalently bonded atoms are often called molecules. Empirical Formulas : Used to describe the relative ratio of atoms in molecules. For example, given the carbohydrate glucose, C 6 H 12 O 6 , the relative ratio is 1:2:1; therefore, the empirical formula is CH 2 O.

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Georgia Institute of Technology | CHEM 1310 | Fall Semester 2009 | Recitation Assignment Mass Spectrometry Sample Mass Spectrum for Magnesium atoms: : An experimental technique that is used to determine the atomic weight of atoms or the weight of compounds and molecules. This technique can be used to determine the relative abundance of isotopes as well. 80% 24 Relative Abundance 25 26 10% Weight Weighted Atomic Mass/Weight for Magnesium = 24(0.8) + 25(0.1) + 26(0.1) = 24.3 g/mol Combustion Analysis/Elemental Analysis (Atomic Contribution)/(Formula Weight) * 100% = Percent Composition : This is a technique used to determine the relative percentage of each atom. For example, given Na 2 CO 3 , the percent composition as indicated with elemental analysis would be as follows: Na atoms: 46.00/106.01 * 100% = 43.39% C atoms: 12.01/106.01 * 100% = 11.32%
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24 August Stoichiometry Recitation - Georgia Institute of...

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